Maximizing the fundamental period of a dithered digital delta-sigma modulator with constant input

Abstract

A digital delta-sigma modulator (DDSM) with a constant input may produce a periodic output with a small fundamental period, resulting in strong tonal output behavior instead of the classically predicted shaped white quantization noise. Pseudorandom dither generators based on linear feedback shift registers (LFSRs) are widely used to “break up” periodic cycles in DDSMs with constant inputs. Pseudorandom dither signals are themselves periodic and can lead to relatively short output sequences from dithered DDSMs. It has been shown, for a MASH comprising a cascade of first-order sections, that the fundamental period of the output signal depends not only on the input and initial condition of the DDSM but also on the initial state of the LFSR. This work extends the analysis to a larger class of DDSM architectures.